Can the Apple Watch with GPS +Cellular be used in Europe?

There are 2 Series 5 cellular radios

• North America (US, Canada, Mexico, Puerto Rico)
• The rest of the world.

Be aware the radios do not do roaming, so they only work in the area serviced by your iPhone cellular carrier

Be aware the warranty is Not international, so you may have to return to the country of purchase for warranty repairs.

ECG must be government approved in the country of purchase and the country where it is used.

Apple Watch ECG countries

https://www.apple.com/watchos/feature-availability/#branded-ecg

You should purchase the watch in the country where you intend to use it, Check this out...https://www.apple.com/watch/cellular/